This invention relates to a process of preparing 1,1,1,3,3,3-hexafluoropropane-2-ol by catalytic hydrogenolysis of hexafluoroacetone hydrate in liquid phase.
As is known, 1,1,1,3,3,3-hexafluoropropane-2-ol (CH.sub.3).sub.2 CHOH (also called hexafluoroisopropanol: so, herein abbreviated to HFIP) is useful as a solvent having peculiar dissolving capabilities and also serves as an intermediate material for various compounds including medicines, anesthetics and agricultural chemicals.
HFIP can be prepared from hexafluoroacetone (abbreviated to HFA) by a reduction or hydrogenation reaction. For example, liquid phase reduction of HFA using sodium boron hydride or lithium aluminum hydride as catalyst gives HFIP. However, this method is not suited to industrial applications. Another method is liquid phase hydrogenation of HFA in the presence of a noble metal catalyst. However, the reactor for use in this method is required to withstand very high pressures (e.g. of the order of 50 kg/cm.sup.2) since the reaction must be carried out under high pressures sufficient to keep HFA (b.p. -28.degree. C.) in liquid phase at the reaction temperature.
Still another method is vapor phase catalytic hydrogenation of HFA. In this case the hydrogenation reaction can continuously be carried out at substantially the atmospheric pressure by passing HFA vapor and hydrogen gas through a catalyst column. However, it is difficult to control the reaction temperature, and undesirable hot spots are often produced in the catalyst column because of generation of heat in the hydrogenation reaction. Furthermore, it is inevitable that the activity of the packed catalyst lowers with the lapse of time, and therefore it is necessary to carry out troublesome procedures for examining possible changes in the quality of the product with the lapse of time and for adjustment of the reaction conditions. Besides, usually it is necessary to use hydrogen gas in considerable excess of the theoretical quantity with a view to accomplishing sufficient conversion of HFA into HFIP. Loss of the excess portion of hydrogen gas leads to a rise in the production cost, but recovery of excess hydrogen gas requires the provision of extra apparatus.
HFA used as the starting material in the above described known processes is a noxious compound which exists as a gas at room temperature. Accordingly, in industrial preparation of HFIP by a conventional method extreme care must be taken in storing, handling and transporting HFA.
As a solution for inconveniences of using gaseous HFA, Japanese patent application primary publication No. 57-81424 and corresponding British patent application publication No. 2,087,383A have proposed to prepare HFIP by vapor phase hydrogenolysis of a hydrate of HFA such as HFA trihydrate, which is liquid at room temperature, using a nickel or palladium catalyst. However, this method too has the disadvantages described above with respect to the vapor phase hydrogenation of HFA (anhydrous).